Surface development of an imagewise exposed emulsion containing silver halide grains with cores chemically ripened in two stages

ABSTRACT

Light-sensitive silver halide emulsion adapted for producing either negative or direct positive photographic images and containing composite grains of silver bromide having internal core portions of chemically ripened silver bromide and external shell portions surrounding such core portions of chemically fogged silver bromide, such emulsion on development with a surface developing agent having a characteristic curve which exhibits a knee portion connecting a generally rectilinear portion of positive gradient and a generally rectilinear portion of negative gradient and is preferably of generally symmetrical configuration. By adjustment of the magnitude of the exposure of the emulsion to light either a direct positive or a negative photographic reproduction is obtained.

United States Patent 11 1 Florens et al. 1451 Jan. 9, 1973 s41 SURFACEDEVELOPMENT OF AN 3,294,540 12/1966 Goffe ..96/87 [M AGEWISE EXPOSEDEMULSION 3,501,307 3/1970 lllingsworth ..96/107 CONTAINING SILVER HALIDEGRAINS WITH CORES CHEMICALLY RIPENED IN TWO STAGES Raymond LeopoldFlorens; Frans Henri Claes, both of Edegem, Delgi lnventors:

. Germany Agfa-Gevaert, Mortsel, Belgium April 2, 1970 Assignee:

Filed:

Appl. No.:

[30] Foreign Application Priority Data April 2, 1969 Great Britain..l7,16l/69 References Cited UNITED STATES PATENTS Berriman ..96/64 um;Frik Moisar, Cologne-Flittard,

OTHER PUBLICATIONS Photolithography, Associated General PublicationsPty, Ltd, Sydney, Australia, 1953, p. 45-46 Primary Examiner-J. TravisBrown Assistant Examiner--Won l-l. Louie, Jr. Attorney-William J. Daniel[57] ABSTRACT Light-sensitive silver halide emulsion adapted forproducing either negative or direct positive photographic images andcontaining composite grains of silver bromide having internal coreportions of chemically ripened silver bromide and external shellportions surrounding such core portions of chemically fogged silverbromide, such emulsion on development with a surface developing agenthaving a characteristic curve which exhibits a knee portion connecting agenerally rectilinear portion of positive gradient and a generallyrectilinear portion of negative gradient and is preferably of generallysymmetrical configuration. By adjustment of the magnitude of theexposure of the emulsion to light either a direct positive or a negativephotographic reproduction is obtained.

7 Claims, 2 Drawing Figures Pmmmm ems 3.709.689

' sum 1 OF 2 FIG. 1

2.7 3.0 i log! I. f) rel.

SURFACE DEVELOPMENT OF AN IMAGEWISE EXPOSED EMULSION CONTAINING SILVERHALIDE GRAINS WITH CORES CHEMICALLY RIPENED IN TWO STAGES The presentinvention relates to the production of photographic images by means of aphotographic silver halide recording material, which depending on theintensity of the image-wise exposure yields a negative or positiveimage.

In the U.K. Pat. Specification Nos. 1,011,062, 1,027,146 and 1,151,781processes for preparing silver halide emulsions containing silver halidegrains that are internally chemically modified have been described.

More particularly according to the process described in the UnitedKingdom Patent Specification 1,027,146 silver halide grains having adifferent interior and surface structure are prepared by interruptedprecipitation and by chemically modifying the interior part of thegrains by adding, e.g., hydrazine as reducing agent after a firstprecipitation stage. Thus, a silver halide emulsion comprising compositesilver halide grains, which consist of a chemically modified -corecovered with a layer of unripened silver halide, is obtained.

It has now been found that a photographic silver halide emulsioncomprising silver halide grains that contain in the interior partripening nuclei or sensitivity specks can be fogged externally to suchan extent that when said grains are incorporated into a photographiccolloid layer and are image-wise exposed in a range of rather lowexposure intensities, a negative image is formed, whereas by image-wiseexposure in a range of higher exposure intensities a positive image isobtained, the developing conditions of both differently exposedphotographic materials being the same.

Silver halide emulsions, which are particularly suited for use accordingto the present invention are obtained by the following steps:

1. the formation of silver bromide grains by mixing in an aqueousgelatin solution a dissolved water-soluble silver salt and a dissolvedwater-soluble alkali metal bromide,

2. the interruption of the precipitation,

3. the chemical ripening of the already formed silver bromide grains,

4. the further mixing of said silver salt and bromide solution, thusforming a shell of unripened silver bromide around the ripened cores,and

5. the fogging of the internally ripened silver bromide grains at theirsurface to such an extent that dependent on the exposure(electromagnetic radiation intensity x time) a substantially negative ora substantially positive image of the original is formed in the silverhalide emulsion layer in the same development conditions.

In the chemical ripening (sensitization) of the said cores noble metalcompounds, e.g., gold compounds, sulphur compounds, reducing compounds,or mixtures of said compounds may be used.

The gold and sulphur sensitization has been described e.g., by C.E.l(.Mees, The Theory of Photographic Process", New York, The MacmillanCompany, revised edition, 1954, pages 1 l2 seq.

The interior ripening of the grains is preferably carried out by meansof a gold sensitizing agent or a reducing agent or with mixtures ofboth.

Particularly preferred for that purpose are thiourea dioxide known alsoas formamidine sulphinic acid and mixtures of water-soluble gold saltsand thiocyanates forming complexes with gold and having a solvent actionon the silver'halide grains, e.g., alkali thiocyanates and ammoniumthiocyanate.

The precipitation of the silver bromide is preferably accomplished bysimultaneously adding the bromide solution and silver salt solution tothe gelatin solution and keeping the pAg-value during the precipitationas constant as possible.

The emulsions containing ripening nuclei in the interior of the silverhalide grains are fogged uniformly at the surface of the grains.

The fogging can be performed with the aid of suitable reducing agents,e.g., hydrazine, tin(lI) salts, ascorbic acid, or formamidine sulphinicacid. The use of formamidine sulphinic acid (thiourea dioxide) andderivatives as sulphur sensitizers with reducing properties is describedin the United Kingdom Patent Specification 789,823 and the U.S. Pat.Nos. 2,983,609 and 2,983,610.

The chemical fogging is the very critical step in the preparation ofphotographic silver halide emulsions suited for use according to thepresent invention. Different concentrations of fogging agent must betried be fore it can be decided which concentration is the best forobtaining a negative or a positive image depending on a properly chosenexposure intensity.

The critical character of said fogging is illustrated in the examples,which prove that for a certain silver halide emulsion and fogging agenta suitable concentration has to be found experimentally.

The development of the exposed silver halide emulsion layers ispreferably carried out by means of a surface developer, e.g., alith-developer, which gives a particularly pronounced differentiationbetween the negative and positive image formation.

A lith-developer is a developing composition foractive-radiation-exposed silver halide, which composition contains anaddition compound of an aliphatic aldehyde or ketone with a hydrogensulphite e.g., formaldehyde hydrogen sulphite, and hydroquinone as thesole developing substance.

The following examples illustrate the present invention.

EXAMPLE 1 An aqueous solution of ammonia was added to 650 ml of a 4percent by weight aqueous gelatin solution at 45C to obtain a pH valueof 9.3. In a precipitating flask were introduced ml of 3N aqueoussolution of potassium bromide and 75 ml of 3N aqueous solution of silvernitrate, at a rate of 10 ml per minute, the pAg value duringprecipitation being adjusted to and maintained at a value correspondingto an E.M.F. of mV (Ag/saturated calomel electrode).

Subsequently 3.5 ml of 10' molar solution of formamidine sulphinic acidwere added. After a digestion time of 30 minutes at 45C the pH waslowered to 6.5 whereupon 1.5 ml of 0.08 aqueous solution of gold(lIl)chloride and 1.5 ml of 2 aqueous solution of ammonium thiocyanate wereadded. The digestion was continued for 10 minutes at 45C.

During the second precipitation an aqueous solution of ammonia was addedto obtain a pH value of 9.3. Then 665 ml of 3N aqueous solution ofpotassium bromide and 665 ml of 3N aqueous solution of silver nitratewere introduced at a rate of 19 ml per min., the

pAg value during precipitation being adjusted to a value correspondingto an E.M.F. of +100 mV (Ag/saturated calomel electrode). The emulsionwas allowed to gel after the addition of 84 g of gelatin and washed inthe usual manner.

After washing, the emulsion was divided in three equal portions A, B,and C, which were fogged respectively in the following way Portion A wastreated for 1 hour at 55C with 1.5 ml

of molar aqueous solution of formamidine sulphinic acid per kg emulsioncontaining 110 g of silver bromide.

Portion B was treated for 1 hour at 55C with 3 ml of 10- molar aqueoussolution of formamidine sulphinic acid Portion C was treated for 1 hourat 55C with 4.5 ml

of 10' molar aqueous solution of formamidine sulphinic acid.

After this fogging step gelatin was added and the pAg was adjusted toavalue corresponding to an E.M.F. of 20 mV (Ag/saturated calomelelectrode). The emulsion ready for coating contained per kg 110 g ofsilver halide, 80 g of gelatin and l g of saponine as wetting agent.Just before coating 500 mg of formaldehyde (hardening agent) was addedper kg of emulsion. The emulsion was applied to a polyethyleneterephthalate support at a ratio of 7.5 g of silver bromide per sq.m anddried.

Test strips were then exposed to incandescent light through a gray testwedge (constant 0.15) and developed for 135 sec at 20C in a developingsolution comprising:

anhydrous sodium sulphite 30 g paraformaldehyde 7.5 g potassiummetabisulphite 2.5 g crystalline boric acid 7.5 g hydroquinone 22.5 gpotassium bromide 1.5 g water to I000 ml The characteristic curvesobtained with the portions A, B, and C respectively are shown in FIG. 1.The exposure intensity expressed in log It relative values is given onthe abscissa, whereas the corresponding density values (D) arerepresented on the ordinate.

EXAMPLE 2 An emulsion was prepared, divided in three portions and foggedas described in Example 1.

Test strips were exposed and developed for 135 sec at 20C in thefollowing developer composition:

p-monomethylaminophenol sulphate 1.5 g anhydrous sodium sulphite ghydroquinone 6 g anhydrous sodium carbonate 80 g potassium bromide 2 gwater to l000 ml EXAMPLE 3 The preparation of the emulsion was carriedout in the way described in Example 1, but the chemical ripening wasperformed with a mixture of 6 ml of 0.08 aqueous solution of gold(lll)chloride and 6 ml of 2 aqueous solution of ammonium thiocyanate. Thesecond precipitation occurred at a pAg value corresponding to an E.M.F.of +20 mV (Ag/saturated calomel electrode).

An analogous result (like B in example 1) was obtained by externalchemical fogging for minutes at 55C with 7 ml of 10" molar solution offormamidine sulphinic acid per kg of emulsion containing g of silverbromide.

We claim:

1. A process of producing negative or direct positive images from thesame light-sensitive photographic material which comprises:

1. forming said material from a silver bromide emulsion prepared by thesteps of:

a. forming silver bromide cores by mixing in an ammoniacal aqueousgelatin solution a dissolved water-soluble silver salt and a dissolvedwatersoluble alkali metal bromide to precipitate grains of silverbromide,

. interrupting the precipitation,

the silver bromide cores with a reducing agent in alkaline medium,lowering the pH to stop that reduction sensitization and continuing thechemical ripening by noble metal compounds in acid medium,

admixing further amounts of the silver salt and bromide solutions aftermaking the solution ammoniacal, thus forming a shell of unripened silverbromide around the ripened cores,

e. fogging the resulting internally ripened silver bromide grains attheir surface by contacting such grains with an amount of chemicalfogging agent sufficient that an emulsion of the thus-treated grainswhen exposed to light through a grey test wedge covering in graduatedsteps a range of log E values from about 0 to at least about 3.00,photographically developed for sec. at 20C in a lith developing solutioncontaining hydroquinone as the sole developing agent and a formaldehydehydrogen sulfite addition compound, and the density values of the thusdeveloped photographic image plotted against the corresponding log Evalues, produces a characteristic curve having an initial positivelyinclined generally straight line portion followed by a knee portion anda negatively inclined generally straight line portion, each of saidpositively and negatively inclined generally straight line portionsextending between a minimum density value not greater than about 0.5 anda maximum density value at least equal to about 1.0;

2. imagewise exposing the thus-formed material to light of an intensityand time giving a log E value in that region of the characteristic curvecorresponding to the desired image, and

3. photographically developing the exposed material in a lith developingsolution containing hydroquinone as the sole developing agent andchemically ripening (chemical sensitization) of i taneously to thegelatin solution while keeping the pAg value during the precipitation asconstant as possible.

5. A process according to claim 1, wherein the fogging is carried out bymeans of a reducing agent.

6. A process according to claim 1, wherein the fogging is effected withformamidine sulphinic acid.

7. A process according to any of the claim 1, wherein the chemicalripening is carried out by means of a mixture of a water-soluble goldsalt and a thiocyanate.

UNKTEEE s'm'ms PATENT @FFIQE @ERTEMQA'EE @E @QRREQEEQN Patent No. 3p709Dated January 9 1973 Inventor(s) Raymond Leopold FLORENS et al It iscertified that error appears in the above-identified patent and thatsaid Letters Patent are hereby-corrected as shown below:

In the Heading of the Patent, correct the inventor's name from "FrikMoi'sar" to Erik Moisar Signed and sealed this 10th day of July 1973.

(SEAL) Attest:

EDWARD M.FLETCHER,JR. Rene Tegcmeyer Attesting Officer ActingCommissioner of Patents

2. The process of claim 1 wherein the characteristic curve of saidemulsion is of substantially symmetrical configuration.
 2. imagewiseexposing the thus-formed material to light of an intensity and timegiving a log E value in that region of the characteristic curvecorresponding to the desired image, and
 3. photographically developingthe exposed material in a lith developing solution containinghydroquinone as the sole developing agent and an addition compound of analiphatic aldehyde or ketone with hydrogen sulfite.
 3. A processaccording to claim 1, wherein the chemical ripening is carried out bymeans of a noble metal compound, a sulphur compound, a reducingcompound, or a mixture of said compounds.
 4. A process according toclaim 1, wherein the bromide solution and silver salt solution are addedsimultaneously to the gelatin solution while keeping the pAg valueduring the precipitation as constant as possible.
 5. A process accordingto claim 1, wherein the fogging is carried out by means of a reducingagent.
 6. A process according to claim 1, wherein the fogging iseffected with formamidine sulphinic acid.
 7. A process according to anyof the claim 1, wherein the chemical ripening is carried out by means ofa mixture of a water-soluble gold salt and a thiocyanate.